1. Field of Invention
The present invention generally relates to a lid for a container that is useful in storing or transporting items such as food, and more particularly, to a selectively detachable container lid having unique venting and denesting features, and a container employing the same.
2. Description of the Related Art
Containers generally have a lid selectively detachable from a bowl and are commonly designed to provide a variety of features, including being reusable, disposable, microwavable, and the like. Generally, these types of containers should be relatively low in cost and easy to use. Depending on their intended use, the containers should be capable of withstanding such varied conditions as those presented by a freezer, microwave, dishwasher and the like.
One problem associated with a conventional, microwavable container stems from the rapid temperature changes that it must endure. The container must be permitted to vent during microwaving due to the high pressures that arise as moisture in the container contents vaporizes and gas temperatures increase. Thus, the container must be left open to some degree during microwaving. However, it is also desirable to keep the bowl covered as much as possible to prevent the contents from splattering the inside of the microwave. One common practice is to remove the lid and place it loosely over the container bowl so that air and steam can escape during microwaving. Another common practice is to only partially remove the lid (i.e., “crack open” the lid) by disengaging only part of the lid from the bowl. This creates an air passage only where the lid has been disengaged from the bowl. Both of these practices generally permit sufficient air and steam to vent during microwaving because the increased pressure within the container will tend to force the container open, increasing any space between the lid and the bowl. However, once microwaving is complete, the steam will cool and the pressure in the container will drop significantly. Because the pressure differential no longer tends to open the container, the above-noted venting practices often do not permit sufficient air to vent back into the container to compensate for the pressure drop. This problem can be aggravated by the accumulation of steam or vapor, which can form a vapor seal between the lid and bowl. A vacuum can result, and the container can be damaged and could ultimately implode.
Another problem results from the fact that when such container lids are thermo-formed, they typically have complementary top and bottom surfaces. When multiple lids are stacked for shipment or storage, adjacent lids often become jammed or interlocked when they nest. This can make the lids very difficult to manipulate, especially by automated handlers in a production line.
There have been many attempts in the art to provide containers that address venting and/or stacking concerns. For example, U.S. Pat. No. 3,091,360 (the “'360 patent”) to Edwards, entitled “Nestable Cup”, provides a reversely-tapered ring adjacent to the bottom of a cup. To prevent stacked cups from nesting too tightly, a shelf is provided at the top of the ring to accommodate the bottom of the ring of an adjacent cup. The ring includes a plurality of wedge-shaped protuberances separated by spaces that act as air vents between adjacent cups to prevent the cups from suctioning to one another. While addressing concerns regarding stacked cups, the design of the '360 patent is not suitable for stacking lids, and it does not address the venting concerns discussed above.
U.S. Pat. No. 3,362,565 (the “'565 patent”) to McCormick entitled “Container Lid”, provides a lid with a sidewall, which has a sealing bead near its base and a shoulder near its top. The sealing bead seals against an internal shoulder provided in a container. When the lids are stacked, the sealing bead rests on the shoulder of the lid below. Notches are intermittently disposed about an outer periphery of the sealing bead. These notches provide a venting passageway through which gases generated in a sealed container can escape when the gas or vapor pressure is sufficient to flex the lid upward at its center, causing a fulcruming action. These notches allow venting when the lid has been fully seated on the container, but do not address the above-noted venting concerns when the lid is loosely seated on or only partially removed from a container.
U.S. Pat. No. 3,589,552 (the “'552 patent”) to Fitzgerald, entitled “Container”, includes a stacking ring on top of a container lid to facilitate separation of stacked lids by a mechanical capping device. A series of interruptions are disposed throughout the stacking ring to prevent the lid from suctioning to an adjacently stacked lid or the mechanical capping device. However, the '552 patent likewise does not address the venting problems that arise when the lid is loosely seated on or only partially removed from the container.
Another approach was taken in U.S. Pat. No. 3,339,786 (the “'786 patent”) to Biglin, entitled “Container and Venting Closure Cap for Same”. A tapered wall with a shelf at its top provides for stacking plural caps. Small ribs or beads across the interior surface of a container sealing channel permit the venting of gases from a capped container. If sufficient internal pressure develops, the gases can freely escape. The '786 patent also does not address venting of a loosely-seated or partially-removed lid.
U.S. Pat. No. 5,147,059 (the “'059 patent”) to Olsen et al., entitled “Seal With Automatic Release”, provides a series of vent-defining protuberances on the inner surface of a vertical, outer sealing portion of a lid. The protuberances engage a container rim to permit venting when the lid is loosely placed on the container. The venting prevents internal/external pressure differentials that might resist the proper seating and removal of the lid. The '059 patent, however, does not address stacking or denesting lids.
U.S. Pat. No. 5,791,509 (the “'509 patent”) to Rush et al., entitled “Uniform Stacking Cup Lid”, provides a lid having an annular trough with an outer wall. The upper portion of the outer wall has a shelf, and the lower portion of the outer wall is negatively sloped and serves as a stacking ring. Positive-draft flutes are spaced periodically around the circumference of the stacking ring to stabilize the stacking ring during thermo-form mold release. The stacking ring of one lid and the shelf of an adjacently stacked lid cooperate to prevent nesting. The '509 patent, however, does not provide a mechanism for preventing a vapor seal between a corresponding lid and bowl.
U.S. Pat. No. 4,753,365 (the “'365 patent”) to Seppala, entitled “Lid With Removable Tab”, provides a lid with a spacer having an outer sidewall, at an upper end of which is an annular seat. The annular seat receives a lower end of the spacer of an above-stacked lid. The '365 patent does not attempt to remedy the vapor seal problem discussed above.
What is needed in the art is a container lid that remains properly oriented and allows venting into and out of the container while being loosely positioned on or partially removed from a bowl, and includes structure that facilitates denesting when stacked with other lids.
In order to simplify design and production, it is desirable to provide a lid in which the structure that facilitates venting of a loosely-placed or partially-removed lid also facilitates denesting of stacked lids.
There is an additional need in the art to provide an inexpensive lid and bowl design that incorporates the above-mentioned objectives.